Issue 5146 - Implement DownloadableSubscription parsing in C++

compiled/String.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 173 matching lines @@
       // This should be more efficient with a lookup table but I couldn't measure
       // any performance difference.
       if (currChar >= u'A' && currChar <= u'Z')
         mBuf[i] = currChar + u'a' - u'A';
       else if (currChar >= 128)
       {
         mBuf[i] = CharToLower(currChar);
       }
     }
   }
+
+  template<typename T>
+  T toInt() const
+  {
+    size_type count = 0;
+    T value = 0;
+    for (size_type i = 0; i < length(); i++)
+    {
+      if (mBuf[i] < u'0' || mBuf[i] > u'9' ||
+          count > std::numeric_limits<T>::digits10)
+        return 0;
+
+      value *= 10;
+      value += mBuf[i] - u'0';
+      count++;
+    }
+    return value;
+  }
 };
 
 class DependentString : public String
 {
 public:
   explicit DependentString()
       : String(nullptr, 0, INVALID)
   {
   }
 
@@ skipping 199 matching lines @@
     if (negative)
       mBuf[pos++] = '-';
 
     for (int i = size - 1; i >= 0; i--)
     {
       mBuf[pos + i] = '0' + (num % 10);
       num /= 10;
     }
   }
 };